The present invention pertains to a slide projector drive mechanism, and more particularly to a slide projector having a drive mechanism for a circular magazine or tray of the type which is equipped with a housing adapted to be rotatably supported on the projector and contains compartments for the slides in a circular arrangement. The external wall of the housing has an approximately h-shaped cross section, in a manner so that two forked parts of the wall are located in close proximity to the one axial side (bottom) of the housing, coaxially spaced at a distance from each other, with the outer part of the wall possessing on its side facing the inner part of the wall a plurality of recesses, corresponding in number to the number of slide compartments, these recesses being distributed uniformly over the circumference and each of them being associated with one of the compartments.
A similar slide projector with a drive mechanism for a circular magazine of the type defined above is known from German Auslegeschrift No. 1,900,326. The slide projector described in detail in German Pat. No. 1,263,342 accomplishes the stepwise rotation of a magazine by a pawl slidable in the radial direction which during its radial advance also performs a movement perpendicular thereto. The distance covered in this lateral movement represents the so-called switching step of the pawl. To rotate the magazine by means of this drive mechansim, at the bottom of the intermediate space formed by the two forked parts of the wall of the magazine housing a serrated slat or rack is arranged, the tooth pitch of which corresponds to the width of the slide compartments. Two rotatably and slidably supported switching levers engage by means of their swtiching projection the serrated slat and protrude with one leg into the slide path of the pawl in the projector. During each switching step of the pawl one leg of one of the switching levers is gripped by the pawl. In this manner, the switching lever is rotated until its switching projection engages between two of the teeth of the serrated slat and is subsequently displaced in the longitudinal direction, while the magazine housing is rotated by a distance corresponding to the width of a slide compartment. In order to prevent the rotation of the housing during the subsequent slide changing process, an indexing pin is additionally provided which under the action of a spring enters one of the recesses in the outer part of the wall of the magazine housing. In the drive mechanism a device is provided which extracts said indexing pin from the recess during the transport of the magazine and then releases the pin following the rotation of the magazine by one switching step, so that it drops into the next recess under the action of its spring, thus locking the housing in the projector with respect to rotation.
In the projector described hereinabove, the drive mechanism may rotate the circular magazine always by only one switching step, thus turning the magazine by the width of one slide compartment, so that now the next slide is located in the exchange or feed plane. If, following the slide being projected, it is desired to view not the slide following in the order of the slide magazine, but rather a slide in a certain slide compartment at an arbitrary location of the magazine, this is possible only by turning the magazine step-by-step by means of the drive mechanism until the desired slide compartment arrives in the exchange or feed plane. This step-by-step rotation of the magazine is highly time consuming and laborious, so that in most cases it will be avoided.